1. Field of the Invention
The present invention relates to a paper sheet stamp apparatus which stamps the surface of a paper sheet conveyed at a constant speed.
2. Description of the Related Art
Paper sheet stamp apparatuses have heretofore been known such as a stamp apparatus for stamping a portion of a mail matter conveyed at a high speed, to which a postage stamp is attached, with a postmark.
This type of the stamp apparatus includes: a conveying belt pair running at a constant speed in a holding state of the opposite surfaces of the mail matter; a stamp hub for stamping a postage stamp portion of the conveyed mail matter with the postmark; and a backup roller rotatably disposed opposite to the stamp hub on a back-surface side of the mail matter. The backup roller presses the mail matter conveyed by the conveying belt pair onto the stamp hub by urging means such as a spring.
The stamp hub substantially has a D-shaped section formed by cutting out a part of an outer peripheral surface, and a letterpress for the postmark is formed on the outer peripheral surface. The cutout portion of the stamp hub is stopped in a home position disposed opposite to a conveying path in an initial state. Moreover, during rotation, the letterpress on the outer peripheral surface of the stamp hub is pressed onto the postage stamp portion of the mail matter to stamp the portion with the postmark.
In general, the stamp hub is rotated by a driving force transmitted from a conveying motor for allowing the conveying belt pair to run. That is, the stamp hub is connected to the conveying motor via a clutch brake. Therefore, the clutch brake is connected in accordance with a timing when the mail matter is conveyed, and the stamp hub is rotated from the home position. Accordingly, the letterpress is pressed onto the postage stamp portion to stamp the portion with the postmark.
However, in the above-described conventional stamp apparatus, the clutch brake is connected and the driving force is transmitted to the stamp hub. It has therefore been difficult to rotate the stamp hub at the same peripheral speed as the conveying speed of the mail matter and to rotate the stamp hub at an appropriate timing. Therefore, when the letterpress of the stamp hub is pressed on the postage stamp portion of the mail matter, a speed difference is generated between the letterpress and mail matter. There is a problem that the postmark warps or deviates.